Board lock and mating flange for PCB retention
The mating flange gives the receptacle a positive stop, so the stack height is repeatable across the assembly line.
Sibling comparison: 1379114-3 vs 1355505-1
The 1379114-3 is identical in every spec except the insulation color is brown instead of black. If your harness drawing calls out brown for a specific circuit branch, that's the one; otherwise the black 1379114-1 is the standard pick. The 1355505-1 is a right-angle version of the same 12-position, 2-row header. If your PCB layout needs the cable to exit parallel to the board rather than straight up, the right-angle 1355505-1 saves the z-height budget.